Electric discharge devices



Aug. 28, 1962 H. DE BOYNE KNIGHT 3,

ELECTRIC DISCHARGE DEVICES Filed April 18, 1960 FIG.|.

147'7'OFPNE'Y Unite States Patent Oflice 3,051,863 Patented Aug. 28, 1962 3,051,863 ELECTRIC DISCHARGE DEVICES Henry De Boyne Knight, Rugby, England, assignor to Associated Electrical Industries Limited, London, England, a British company Filed Apr. 18, 1960, Ser. No. 22,778 Claims priority, application Great Britain Apr. 27, 1959 3 Claims. (Cl. 313-189) This invention relates to electric discharge devices of the kind in which the discharge has the characteristic of an arc, and occurs between an electron-emitting electrode and an anode in an envelope which contains an ionisable medium at a pressure, under operating conditions, which is generally not greater than two thousand microns of mercury.

In the invention described and claimed in application Serial No. 839,937 filed September 14, 1959 by me and assigned to the assignee of the present application, I have disclosed an electric discharge device of the kind above set forth in which there is interposed between a heated cathode and the anode a barrier electrode having at least one aperture through which the discharge is caused to pass, the material of which the barrier electrode is composed and the size of the aperture(s) therein being such that the passage of an initial discharge between the heated cathode and the anode through the aperture(s) cause the formation of an electron-emitting region on the barrier electrode to which the arc discharge transfers from the heated cathode, which discharge is not limited to that obtainable from the heated cathode and is utilised as the main discharge current of the device.

Thus the heated cathode has only the auxiliary function of initiating discharge in the device, the conducting member forming the barrier electrode being connected to the external circuit and functioning as the main cathode of the device, current flow to it from the anode being unrestricted by the aperture described above.

In an electric discharge device of the kind set forth, according to the invention, a main discharge space between a main cathode and an anode is separated by the main cathode from an auxiliary discharge space in which an auxiliary electron emitting cathode is located, the electron emission from the main cathode being normally incapable of supporting a discharge to the anode until ionisation produced in the auxiliary discharge space by an initiating discharge between an auxiliary anode and the auxiliary cathode has taken place, the main cathode being apertured to enable the ionisation produced by the initiating discharge to initiate the formation of a cold emission spot at which the main discharge to the anode originates.

The auxiliary anode may be located within the auxiliary discharge space, or in the main discharge space. In the former case, the ionisation arising from the initiating discharge is effective, through the aperture in the main cathode, to cause suflicient ionisation to occur in the main discharge space in the vicinity of the main cathode to encourage the main cathode to be electron-emissive and support a discharge from the main anode to the main cathode. In the latter case, the initiating discharge takes place through the aperture in the main cathode so that electron-emission from the main cathode is directly initiated.

The starting of an initiating discharge between the auxiliary anode and the auxiliary cathode may be controlled by an auxiliary electrode located in the auxiliary discharge space, the auxiliary anode being then maintained at a potential with respect to the auxiliary cathode such that a discharge between them will occur in the absence of a hold-off potential on the auxiliary electrode; al-

2 ternatively, the starting of an initiating discharge between the auxiliary anode and the auxiliary cathode may be produced by applying a potential of suitable value positively to the auxiliary anode only when the initiating discharge is required to take place.

It is possible for the function of the auxiliary anode to be performed by the main cathode acting as an auxiliary anode with respect to the auxiliary cathode. In this case, the auxiliary anode is omitted and a suitable voltage is applied between the main cathode and the auxiliary cathode to cause an initiating discharge to take place in the auxiliary discharge space.

The invention will be more readily understood from the following description of the accompanying drawings, in which:

FIG. 1 shows diagrammatically in cross-section an electric discharge device embodying the invention and employing an auxiliary anode located in the auxiliary discharge space in which the auxiliary cathode is located and embodying a control electrode for controlling the production of the initiating discharge, and

FIG. 2 is one suitable form of circuit arrangement which can be employed for operating the device exemplified in FIG. 1.

Referring to FIG. 1, a vacuum-tight envelope 1 contains a filling of gas and/or vapour at a low pressure, generally not above 2000 microns Hg. Inside the envelope is an electrode system comprising an anode 2, an auxiliary thermionically-emitting cathode 3, a main cathode 3, :a main cathode 4 and an auxiliary anode 5. Main cathode 4 separates the main discharge space between cathode 4 and anode 2 from the auxiliary discharge space in which the auxiliary cathode 3 and auxiliary anode 5 are located, main cathode 4 being shown as a cross bafile of conducting material held in a sheet metal cylinder 7 and having one or more apertures 6. The surface of cathode 4 may be provided, at least in the neighbourhood of aperture 6, with insulation-conductor combinations as described in the specification of the prior patent application hereinbefore referred to. The auxiliary anode 5, which may conveniently be a cylinder, wire or disc, held on a lead insulated by insulation sleeve 8, is shown in such a position that an initiating discharge may be passed between it and the thermionically-emitting cathode 3; such a discharge may be produced by making auxiliary anode 5 positive with respect to 3, assuming the latter to be heated to emitting temperature, the initiation being controlled either by timing the application of potential difference between auxiliary anode 5 and cathode 3, or by the application of a suitable potential to a control electrode 9. Auxiliary anode 5 may alternatively be located in the main discharge space, i.e. in the space between ca-thode 4 and anode 2; in this case, the initiating discharge passes through aperture 6. In either case, ionised particles from the initiating discharge find their Way to the surface of the cathode 4 in the neighbourhood of the aperture 6, which is required for the formation of a cathode spot on main cathode 4.

The auxiliary cathode 3 is shown as a thermionicallyemitting cathode, heated to a suitable emitting temperature by a separate heating supply. Any other source of adequate electron emission may be used alternatively, such as a cathode spot produced on the surface of a mercury pool.

The functioning of the device is illustrated by the circuit diagram of FIG. 2. The main anode 2 and main cathode 4 are connected to a main supply circuit through leads 10, the load on the circuit being represented by 11. 'The auxiliary anode 5 and the auxiliary cathode 3 are connected through a current limiting impedance 14 to a supply source shown as a capacitor 12 which can be charged through rectifier 13 and current limiting impedance 18. The control electrode 9 is connected to a circuit 15 whereby its potentialcan be brought to a required value when a discharge is to be initiated between auxiliary anode and auxiliary cathode 3. Ionised particles from this discharge diffuse to the surface of main cathode 4 and if anode 2 is at a suitable potential positive with respect to cathode 4, cathode spots are formed on the latter and current flows in circuit 10, provided the current possible is adequate for spot formation.

If impedance 16 and/ or capacitance 17 are connected between auxiliary cathode 3 and main cathode 4, a discharge current may pass in circuit from the main anode 2, via cathode 3 and impedances 16, 17, when the discharge passes from auxiliary anode 5 to cathode 3, and prior to the formation of the cathode spot on main cathode 4. Impedance 16 may, however, consist of the leakage resistance and impedance .17 of the stray capacitance between the main circuit 10 and the auxiliary circuit of electrodes 3, 5 and 9.

The circuit of FIG. 2 is a non-limiting illustration of the means of initiating the initiating discharge between auxiliary anode 5 "and cathode 3. Any other suitable circuit may be adopted, and the use of control electrode 9 is optional in the operation of the device according to the invention.

What I claim is:

1. An electric discharge device comprising a sealed envelope filled with :a gaseous ionizable medium at low pressure, a main cathode and an anode defining a main discharge space located within said envelope, an auxiliary discharge space completely separated from said main discharge space by said main cathode, an auxiliary anode and an auxiliary cathode located in said auxiliary discharge space, the electron emission from the main cathode being normally incapable of supporting a discharge to the anode until ionization produced in said auxiliary discharge space vbetween said auxiliary anode and said auxiliary cathode has taken place, said main cathode being rapertured to enable the ionization produced by the initiating discharge to initiate the formation of a cold emission spot on the main cathode at which the main discharge to the anode originates, and said main cathode being composed of an intimate sintered association of particles of insulating and conducting material at least in the vicinity of said aperture to facilitate the formation of said cold emission spot.

2. An electric discharge device as claimed in claim 1 in which an auxiliary electrode is located in the auxiliary discharge space to which an initiating discharge control potential is adapted to be applied, the control electrode being normally maintained at a potential such as to inhibit a discharge irom the auxiliary cathode.

3. An electric discharge device comprising a sealed envelope filled with a gaseous ionizable medium at low pressure, an anode and an auxiliary cathode spaced apart in said envelope, a tubular electrode surrounding the path between said anode and said auxiliary cathode, an apertured main cathode extending transversely completely across the interior of said tubular electrode .to separate an auxiliary discharge space located between said auxiliary cathode and said main cathode from a main discharge space between said main cathode and the said anode, the electron emission from the main cathode being normally incapable of supporting a discharge to the anode until ionization produced in said auxiliary discharge space between said auxiliary anode and said auxiliary cathode has taken place, said main cathode .being apertured to enable the ionization produced by the initiating discharge to initiate the formation of a cold emission spot on the main cathode at which the main discharge to the anode originates, and said main cathode being composed of an intimate sintered association of particles of insulating and conducting material at least in the vicinity of said aperture to facilitate the formation of said cold emission spot.

References Cited in the file of this patent UNITED STATES PATENTS 2,158,564 Meier May 16, 1939 2,578,571 Meier Dec. 11, 1951 2,889,481 Stieritz June 2, 1959 2,900,550 Fowler Aug. 18, 1959 

